1. Field of this Invention
This invention relates to a process for sorting coarse to fine materials according to their chemical composition, in which samples are taken and analyzed, and in which the transporting and/or further processing of the materials is controlled according to the results of the analysis.
2. Prior Art
When mining mineral raw materials, it is necessary for an economical process that the composition of the raw material be constantly controlled. On the one hand this determines the proportion of waste rock or pay gravel, and on the other it is often necessary to keep certain disturbing admixtures under control. For these measurements, a sample must be obtained for analysis which is as representative as possible of the batch of raw material under consideration. Normally, random samples of the raw material are taken using a shovel or some other grabbing tool. The sample is then prepared for the actual chemical analysis (ground homogenized). This presents two important problems, namely:
obtaining a really representative sample; and
conducting the analysis in such a short time that, depending on the result of the analysis, it is possible to intervene in the transporting or further processing of the materials.
Since the total analysis (taking the sample, preparation and chemical analysis) takes a relatively long time (at least ten minutes), it has so far only been possible to take samples and intervene in the process according to the results of the analysis at intervals which are too great. The result of this in mining iron ore in a large underground mine, for example, is the undesired mixing of ores having different phosphorus contents. This mixing of ores causes the yield of low-phosphorous ore to fall far below what is possible from a geological point of view. The mixing occurs directly at the mining site. The blasted ore is transported to shafts approximately 40 to 200 m away using power shovels (one shovel holds about 8 tons). A sample weighing around 1 kilogram is taken only from about every tenth shovel using a grabbing tool. This sample is ground, sifted and magnetically separated, with one part of it then being dried; and a part thereof is measured and analyzed by wet chemical methods. On the basis of the results of this analysis, all further shovels are tipped into the shaft provided for the grade analyzed until the results of the next analysis are available, although the composition of the material generally changes from one shovel to the next. The phosphorus content, which is an important determinant of quality, may vary by a factor between 10 and 100.